The Book of Menstruation
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا سُفْيَانُ، عَنِ الضَّحَّاكِ بْنِ عُثْمَانَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَجُلاً، مَرَّ وَرَسُولُ اللَّهِ صلى الله عليه وسلم يَبُولُ فَسَلَّمَ فَلَمْ يَرُدَّ عَلَيْهِ .Ibn Umar reported:A person happened to pass by the Messenger of Allah (ﷺ) when he was making water and saluted him, but he did not respond to his salutation
From Sahih Muslim, whose reports the scholars accept as authentic.